Apparatus suited for extreme ultraviolet lithography, comprising a radiation source and a processing organ for processing the radiation from the radiation source, and a filter for suppressing undesired atomic and microscopic particles which are radiated by a radiation source.
The invention relates to an apparatus comprising a radiation source and a processing organ for processing the radiation from the radiation source, wherein a filter is placed between the radiation source and the processing organ, which filter comprises a plurality of foils or plates.
Such an apparatus may be used in the production of integrated circuits, that is to say in a lithographical application. The invention may also be applied in various other fields. For a good understanding of the invention, however, a lithographical application will serve well as illustration. Continuous attempts are made to make integrated circuits smaller and smaller in order to improve the processing speed of the integrated circuits.
According to the prior art, such integrated circuits are manufactured chiefly by using lithography with visible and ultraviolet light. With these known technologies, it is possible to manufacture integrated circuits that may be as short as 120 nanometers. The ultraviolet light used with said circuits has a wavelength of 193 nanometers. The known techniques do not allow a further decrease of the dimensions of the integrated circuits, and a possible solution is the use of lithography on the basis of extreme ultraviolet light. Such light has a wavelength of 13 nanometers. The known optical elements cannot be used at this wavelength. The known mirrors and lenses absorb too large a portion of the extreme ultraviolet light. In order to allow for this, the processing organ for processing the radiation from the radiation source is a multi-layer mirror which consists of 40 or more molybdenum layers alternating with silicon layers.
In such an apparatus for extreme ultraviolet lithography a laser plasma source is used to generate a plasma by heating an object by means of a laser source of high energy density, for example of at least 1011W/cm2. The object heated by the laser will function as source of secondary emission of mainly shortwave radiation. However, this will also release undesirable particles and atoms producing the effect of debris in the apparatus. The objective of the invention is to prevent the production of said debris.
WO 96/10324 discloses such an apparatus for the generation of radiation. This apparatus uses a fast rotating target which is heated by the laser source and which produces the secondary emission. Due to the kinetic energy of the particles formed from the plasma on the rotating target, this apparatus has a filtering effect in respect of the so-called macro-particles. However, trapping atoms, and in particular the fastest micro-particles, is not possible in this known apparatus.
U.S. Pat. No. 4,837,794 concerns a filter apparatus comprising a radiation source and a processing organ for processing the radiation from the radiation source, wherein a filter is placed between the radiation source and the processing organ, which filter comprises a plurality of foils or plates, including a baffle for diffusing hot gases and directing them away from a window of sight. Due to the placement of the baffle, the said window of sight is rather narrow.